(1) Field of the Invention
The invention concerns a field testing apparatus and a method for determining the dynamic elastic modulus of asphalt. A preferred field of application of the invention is the determination of the dynamic elastic modulus of asphalt in asphalt poured as pavement or as installed asphalt.
The dynamic elastic modulus of asphalt poured as pavement or as installed asphalt is typically determined in accordance with the splitting tension-swelling test. For this purpose, a cylindrical test specimen is taken from the asphalt layer to be tested, to which a sinusoidal pressure swelling load is introduced via two diametrically opposite load input rails arranged on the outer surface of the cylindrical specimen (see operating instructions for determining the stiffness and fatigue behavior of asphalts with the splitting tension-swelling test as input variable for the dimensioning, AL Sp-asphalt 09, Research Institute for Roads and Transportation, Issue 2009, pp. 10-16). The tensile stress produced in the test specimen causes significant material fatigue and ultimately the fracture of the test specimen.
The test specimen is loaded with a force-controlled, harmonized sinusoidal swelling load without load pauses at different stress levels and load frequencies, wherein the load is continuously applied and increased until macro cracks appear in the test specimen. The test force and the deformation of the test specimen transverse to the direction of the test force are detected. The dynamic elastic modulus is calculated from these values. When the dynamic elastic modulus increases of under repeated loading of the test specimen, the curve of the dynamic elastic modulus as a function of the number of applied loads is a measure for the stiffness of the asphalt; conversely, a decrease of the curve of the dynamic elastic modulus as a function of the number of loads is a measure for the fatigue behavior of the asphalt. The splitting tension-swelling test is complicated and can only be performed in the laboratory, so that test results are available only after a considerable time after the samples have been removed and are related to permanent the damage in the asphalt surface to be tested due to the sample removal. This test is therefore not suitable as a field test.
(2) Description of Related Art
DE 10 2008 035 565 A1 mentions that the load carrying capacity of asphalt in an uncured state can be determined by using a device with a drop weight according to technical test method TP BF-StB Part B 8.3. In particular, the dynamic elastic modulus, in DE 10 2008 035 565 A1 called dynamic deformation modulus, of the test plenum is determined. A drop weight tester according to the above test method includes a load plate having a diameter of 300 mm and a mass of 15 kg, and a load device composed of drop weight, guide rod, spring element and release device. The mass of the drop weight is 10 kg, the total mass of the guide rod is 5 kg. The drop weight acts on the load plate with a force of 7.07 kN. An acceleration sensor, which is configured to measure the movement of the load plate placed on the test plenum that is caused by the force impact of the drop weight, is coupled to the load plate. The dynamic elastic modulus of the test plenum is determined from the movement of the load plate, i.e. from the movement of the test plenum caused by the force impact. However, the determined dynamic elastic modulus is not a specific characteristic value of the asphalt in the asphalt layer, but rather a characteristic value that describes the dynamic behavior of the entire system of the layer structure below the test plenum, i.e. of the compacted soil, the support layers built on top of the compacted soil and the final layer of asphalt. This drop weight cannot be used to determine the dynamic elastic modulus as a characteristic material parameter of the asphalt in the asphalt layer.